The present invention relates to a method of channel allocation.
With wireless cellular telecommunications networks, the area covered by the network is divided into a plurality of cells. Each cell has a base station which communicates with mobile stations in the cell associated with the base station.
However, in order to increase the available capacity in wireless telecommunications networks, microcells have been proposed. A microcell is typically used in urban environments and overlies larger cells which are referred to as macrocells. A microcell may typically cover a radius of 200 m. A microcell will have a base station with a transmitting and receiving antenna mounted below the height of the surrounding rooftops and the transmit power will be lower than that for macrocells. These microcells can be provided at traffic hot spots (an area with a high traffic density). Thus micro cells allow areas with high capacity requirements to be targeted.
It has been proposed that microcells share channels with the macrocells. Accordingly, various method have been proposed to determine which channels are available to the microcells. These methods typically involve the use of network planning tools which are cumbersome and time consuming.
Reference is made to WO98/26623 which describes a method of allocating a frequency to a cell in a cellular system. A cell is surrounded by a plurality of neighbouring cells. A measuring signal is transmitted from the cell to the neighbouring cells. The cells have a plurality of mobile stations which are served by a base station. The cellular radio system has first field strength measuring means for measuring the disturbance field strength, that is the magnitude of the disturbance caused by neighbouring cells in the new cell. Second field strength measuring means measure the field strength of the channel serving the mobile station. Ratios of field strength to disturbance field strength are determined, the ratio being utilised for forming a disturbance probability distribution which is used to allocate a suitable frequency to the cell. No reference to microcells and the associated problems are included in this reference.
xe2x80x9cA practical approach to channel borrowing for microcells in GSM systemsxe2x80x9d, V Wille, H Multimaki and S Irons was presented at the 48th Annual International Vehicular Conference (VTC""98) on behalf of the present applicant. This document proposed a method for identifying the least interfered channel for microcells so that channels for the microcell can be shared with the macrocells.
It is an aim of embodiments of the present invention to provide a method and apparatus for channel allocation which improves on the methods of the prior art. Embodiments of the present invention may improve on the method described in the paper mentioned hereinbefore.
According to one aspect of the present invention, there is provided a method of allocating a channel in a cell of a cellular network comprising said cell and a plurality of other cells, said method comprising the steps of:
receiving in said cell, a plurality of signals from at least one other cell;
determining the average signal strength of said plurality of signals and the standard deviation for said signals;
adding the average signal strength to the standard deviation to provide information; and
using said information to determine one or more channels to be used in said cell.
According to a second aspect of the present invention, there is provided a network element for providing information for use in allocating a channel in a cell of a cellular network comprising said cell and a plurality of other cells, said network element comprising:
means for receiving information on the strength of a plurality of signals from at least one other cell;
means for determining the average signal strength of said plurality of signals and the standard deviation for said signals;
means for adding the average signal strength to the standard deviation to provide said information.
By using the standard deviation information, it is possible to improve the determination of which channel is to be used in a cell.
Preferably, the method includes the step of multiplying the sum of the standard deviation and the average signal strength by the number of the plurality of signals, the resulting information being used in the using step. Preferably, the information is determined for each of a plurality of other cells. The information determined for each other cell may be normalised with respect to the information for that cell and the other cell(s) for which information has been determined.
Preferably said cell has at least one station associated therewith, said at least one station being arranged to measure the strength of the signals received from the at least one other cell, the measurements being used to determine the average signal strength. The at least one station may be a mobile station.
A plurality of stations may be provided in the cell, each of said plurality of stations being arranged to measure the strength of signals received from said at least one other cell, the measurements being used in determining the average signal strength. The reference signals from at least one other cell may be received and the average strength of the reference signals may be determined.
A plurality of channels may be used in one of said other cells and the strength with which the channels would be received in said cell is determined from the information based on said reference signals. Preferably, at least one channel is used in more than one of said other cells and the strength which said at least one channel would be received in said cell is determined by adding the contribution for the at least one channel from the said more than one of said other cells together.
Preferably, in said using said information step, one or more of the channels used by at least one or more of the plurality of other cells and which are not received in said cell or received with a lower strength are allocated to said cell. Preferably, the received signals are from a base station in the respective at least one other cell. The cellular network may be a GSM network. The received signals may be from a base station in the respective at least one other cell and the signals may be the BCCH channel of the respective base station.
The cell may be a microcell. The cell may alternatively or additionally be an inbuilding cell.